upower

UPower is a power management daemon for Linux and other Unix-like operating systems. It provides a unified interface for monitoring and managing power sources such as batteries, AC adapters, and uninterruptible power supplies. Developed as part of the freedesktop.org project, UPower exposes power information to user-space applications through the D-Bus interprocess communication system, enabling desktop environments and utilities to obtain consistent power status data.

UPower runs as a background service (upowerd) and gathers data from the kernel’s power-supply interface (typically via ACPI and related hardware interfaces). It maintains a tree of power devices, including batteries, AC, and UPS devices, and exposes a manager object along with per-device objects over D-Bus. Each device provides properties such as OnBattery, OnLine, Percentage, TimeToEmpty, TimeToFull, and sometimes additional metrics like voltage or design capacity. The daemon emits signals when device state or properties change, allowing user interfaces to update in real time.

Integration and usage: UPower is used by major desktop environments such as GNOME and KDE to populate battery indicators, display estimated remaining time, and drive power-saving policies. It replaces earlier HAL-based approaches by offering a standardized, vendor-agnostic interface for power information. UPower can handle multiple batteries and UPS devices and can report diagnostic information such as design capacity and last full charge when available.

Development and licensing: UPower is open-source software released under the GPL, typically GPL-2.0-or-later. It is maintained by the FreeDesktop community and implemented in C using GLib, with a focus on providing a stable, cross-desktop power-management interface via D-Bus.